Carburetor for automotive vehicles

ABSTRACT

A carburetor for automotive vehicles having improved performance characteristics in supplying fuel-air mixtures to the engine of the vehicle, including an auxiliary fuel-air supply arrangement and regulating valve which is responsive to instantaneously varying operating conditions of the engine to supply correspondingly adjusted quantities of fuel-air mixture thereto.

United States Patent [191 Hartel et a1.

Appl. No.: 191,625

Foreign Application Priority Data Oct. 24, 1970 Germany G 70 39 342.9

US. Cl. 261/41 D, 123/97 B, 261/44 R, 261/69 R Int. Cl. F02m 9/06 Fieldof Search 261/44 R, 69 R, 41 D; 123/119 R, 97 B References Cited UNITEDSTATES PATENTS 8/1943 Chisholm 261/41 D Oct. 16, 1973 2,447,264 8/1948Beardsley, Jr 261/69 R 3,190,623 6/1965 Ball 261/39 B 3,252,539 5/1966Ott et a1 261/41 D 3,265,373 8/1966 Walker et a1. 261/41 D 3,272,4889/1966 Bickhaus... 261/69 R 3,304,068 2/1967 Thomas 261/41 D 3,408,05410/1968 Walker 261/69 R 3,450,115 6/1969 Toda et al'..... 261/44 R3,472,494 10/1969 Seiden 261/41 D FOREIGN PATENTS OR APPLICATIONS2,005,063 8/1970 Germany 261/44 R Primary Examiner-Tim R. MilesAttorney-Eric H. Waters et a1.

57 ABSTRACT A carburetor for automotive vehicles having improvedperformance characteristics in supplying fuel-air mixtures to the engineof the vehicle, including an auxiliary fuel-air supply arrangement andregulating valve which is responsive to instantaneously varyingoperating conditions of the engine to supply correspondingly adjustedquantities of fuel-air mixture thereto.

6 Claims, 2 Drawing Figures "Patented Oct. 16, 1973 3,765,658

2 Sheets-$heot 1 Patented Oct. 16, 1973 3,765,658

2 Sheets-Sheet 2 FIG 2 1 CARBURETOR FOR AUTOMOTIVE VEHICLES FIELD OF THEINVENTION This invention relates to a carburetor for automotive enginesor the like and, more particularly, to a carburetor providing forimproved performance characteristics in response to rapidly orinstantaneously changing engine operating conditions.

Various carburetors are presently known, which include suitableinstallations providing fuel-air mixtures for normal engine operation,with these installations being generally designated as the carburetorprimary systems. The fuel-air mixture outlet conduit or passageway ofthe primary system leading to the engine generally includes a mixturethrottle, which is selectively or arbitrarily actuatable, and which isusually constituted of a throttle valve. Furthermore, presently usedcarburetors also frequently include devices providing fuel-air mixturesfor the idling and drive operating modes of the engine, essentiallyconsisting of a calibrated fuel supply conduit, a calibrated air supplyline, and an idling or auxiliary fuel-air mixture conduit which connectsinto the fuel-air mixture outlet conduit leading to the enginedownstream of the mixture throttle valve. The fuel supply conduits andair supply line for the engine idling and drive operating modes may alsobe combined with the fuel-air supply components of the carburetorprimary system.

DESCRIPTION OF THE PRIOR ART In utilizing prior art carburetors, it hasbeen found that when the idling automotive engine is subjected to loadsfrom auxiliary components, such as, for example, automatic drives orengine accessories, difficulties arise in supplying an adequate fuel-airmixture to the engine. These difficulties result in the rotational speedof the engine dropping below a required minimum value for the unloadedor idling operating mode of the engine, which may cause the stalling ofthe engine.

SUMMARY OF THE INVENTION It is, accordingly, an object of the presentinvention to provide a novel carburetor which avoids the limitations anddrawbacks encountered in the prior art.

It is a further object of the invention to provide a carburetor having afuel-air mixture output which will maintain the engine idling speed at aconstant value, independently of rapid changes or fluctuations in theloads imposed on the automotive engine through auxiliary components andaccessories.

Another object of the invention is to provide a novel carburetor whichwill supply during drive operating modes requiring increased enginerotational speeds, a controlled quantity of fuel-air mixture to theengine which is larger than the quantity required for the engine idlingmode.

In accordance with the present invention, the novel carburetor havingthe improved fuel-air flow characteristics is provided with a regulatingvalve which is positioned at the orifice of the idling or auxiliaryfuel-air mixture conduit, and with the valve having a crosssectionalflow through area which is automatically increased in response to anincrease in the fuel-air suction tube pressure and decreased in responseto .a drop in the pressure.

In order to attain this operating objective, the regulating valveincludes an actuating device which consists of a closed membrane housinghaving a membrane interiorly thereof so as to form a first membranechamber which is connected to ambient or atmospheric air, and a secondmembrane chamber which is connected by an evacuated or reduced-pressureconduit to the fuel-air mixture outlet conduit of the primary system ata point downstream of the mixture throttle. The membrane is subjected tothe pressure of the fuel-air suction tube in opposition to theadjustable tensile force of a spring in the membrane housing.

The regulating valve includes adjusting elements for themembrane-loading spring and for the quantity of fuel-air mixture beingsupplied to the engine. The adjusting elements consist of twoconcentrically positioned adjusting screws which extend through the wallof the membrane housing. The larger or outer adjusting screw facilitatesthe adjustment of the membrane spring, whereas the smaller adjustingscrew regulates the operating stroke of the valve and thereby controlsthe quantity of fuel-air mixture flowing therethrough.

The idling engine is frequently loaded in a rapid or instantaneousmanner through an auxiliary engine component or accessory. Consequently,fuel-air suction pressure will be correspondingly rapidly increased. Inorder to correlate the action of the regulating valve with the suddenpressure increase without undue delay, a generally unhindered flow mustbe provided in the conduit leading toward the membrane housing. This isachieved by providing, at the juncture between the reduced-pressureconduit and membrane housing, a return valve, which only allows the flowto be toward the membrane housing upon the reduced-pressure conduitreaching a higher pressure than the pressure prevailing within themembrane housing.

Any unrestricted flow through the reduced-pressure conduit in thereverse direction is undesirable in order to avoid over-compensation inthe closing direction of the regulating valve which would result influctuation or sag of the operating rotational speed of the engine. Therequired effect is provided by a calibrated by-pass passageway orconduit located upstream of the return valve which provides a continuousflow connection between the reduced-pressure conduit and the membranechamber, bridging the return valve.

At engine drive, in effect, when the moving vehicle drives the connectedengine at a rotational speed in excess of its idling speed, it isdesirable to havean increased quantity flow of the fuel-air mixturetoward the engine. Accordingly, a further feature of the invention liesin the provision of a switching valve at the juncture between thereduced-pressure conduit and the fuel-air mixture outlet conduit of theprimary system at a point downstream of the mixing throttle, adapted toselectively connect the reduced-pressure conduit with the fuel-airmixture outlet conduit of the primary system or with the ambientatmosphere.

The actuation of the switching valve is dependent upon the engine speedin a manner whereby the'reduced-pressure conduit is connected withambient atmosphere when the engine exceeds a predetermined speed, andconnected to the fuel-air mixture outlet conduit of the primary systemat all lower engine speeds. As soon as the reduced-pressure conduit isvented to the ambient atmosphere, both membrane chambers of the membranehousing are subjected to an equal pressure. This causes the springacting on the membrane to be unloaded, thereby increasing thecross-sectional flow area of the regulating valve to its greatest value.

The actuation of the switching valve may be effected, as is known, by asuitable electromagnet which may be activated or deactivated by means ofan electric or electronic engine RPM counting switch.

The actuation or selective positioning of the switching valve may alsobe dependent upon the pressure in the suction conduit generated inresponse to the speed of the engine, whereby the reduced-pressureconduit is connected to the ambient atmosphere when the pressure in thesuction conduit drops below a predetermined value, and connected to thefuel-airmixture outlet conduit of the primary system downstream of themixing throttle upon the pressure in the suction tube reaching highervalues. The actuation of the switching valve is obtained with theassistance of a membrane housing device, the latter of which isresponsive to the pressure in the suction conduit. This mode ofswitching valve actuation has the advantage in that it is not dependenton electrical energy. The value of the suction tube pressure may becontrolled within definite parameters having predetermined tolerancesallowing for fluctuations in the engine speed.

The connecting point or juncture between the reduced-pressure conduitand the fuel-air mixture outlet conduit of the primary system ispreferably located outside the mechanical operating range of thefuel-air mixing throttle valve. This may present difficulties in that,depending upon the particular construction of the engine, the regulatingvalve may be opened to an excessive degree inasmuch as, during thechange of engine operation from idling to drive mode, the suction tubeor conduit pressure increases by a considerable amount. Thesedifficulties may be readily avoided by locating the connection betweenthe reduced-pressure conduit and the fuel-air mixture outlet conduit ofthe primary system within the mechanical operating range of the mixingthrottle valve. Since this installation permits the mixture throttlevalve to be easily opened during change-over from engine idling to driveoperating mode, the edge of the movable valve portion extends over theoutlet orifice of the reduced-pressure conduit. The mixture being suckedinto the engine, flowing past the edge of the valve at a high flowvelocity, reduces the level of the pressure prevailing in thereducedpressure conduit to a point below that in the suction tube orconduit, so as to prevent the full effect of the v increased pressure inthe suction tube being felt by the regulating valve in response to theopening of the throttle valve.

An improved sequence in the change of'engine operating modes may beobtained by connecting the reduced-pressure conduit with the fuel airmixture outlet conduit of the primary system downstream as well asupstream of the mixing throttle valve so as to locate the connectionwithin the mechanical operating reach of the mixing throttle valve.

The valve seat and closure members of the regulating valve areconstructed to facilitate the mixture of the fuel and air to beintroduced into the suction conduit in a well-distributed manner. This,for example, is the case when the valve seat and closure members of theregulating valve have essentially conical configurations. The advantagesof the invention consists not only in that the engine and idling speedis maintained constant under variable loading conditions, and thestalling of the engine is avoided upon sudden loading thereof. Anotheradvantage lies in the inclusion of an automatic compensator forbarometic pressure increases. Thus, with the increasing barometricpressures, the difference between the suction tube pressure and theatmospheric pressure is reduced, and as a result this will increase theflow cross-sectioned area of the regulating valve. In the absence of aregulating valve according to the invention, the idling speed of theengine would be reduced in response to a reduced fuel-air mixture flowinto the cylinders of the engine. With the inventive regulating valvebeing utilized, the rate of filling of the cylinders of the engine isincreased in response to the increased cross-sectional flow area of theregulating valve. Through suitable calibration of the measurements ofthe regulating valve, the idling speed of the engine may be closelymaintained at a constant level independently of the then presentbarometric pressure.

BRIEF DESCRIPTION OF THE DRAWINGS Reference may now be had to theaccompanying drawings showing exemplary embodiments of the invention, inwhich:

FIG. 1 illustrates a cross-sectional view of a carbure tor according tothe present invention; and

FIG. 2 illustrates a cross-sectional view of a second embodiment of acarburetor including a regulating valve according to the invention, andproviding for a piston arrangement controlling the fuel-air suctionconduit flow cross-section.

DETAILED DESCRIPTION Referring now to the drawings, the carburetorincludes the housing 11 having an air inlet conduit 12 of generallycircular cross-section, and a fuel-air mixture outlet conduit 13, alsoof circular cross-section. A slide piston 14 extends verticallydownwardly into the hous ing 11 of the carburetor. When the slide piston14 is completely located within the carburetor housing 11, the inlet ofair is largely throttled. Through movement of the slide piston 14, asmaller or larger flow crosssection is provided as required. The liftingof the slide piston 14 is caused by the vacuum or reduced pressureacting on a membrane 15 across a bore 97.

The membrane 15, which is formed of a rubberized elastic material or arubber web, is connected to the slide piston 14 in a gas-tightrelationship. The outer peripheral rim of the membrane 15 is clamped ina gassealed relationship between the carburetor housing 11 and acarburetor cover 16.

At its lower end, the slide piston 14 carries a jet needle 17 whichextends into a jet orifice 18. The jet orifice 18 is movably or slidablypositioned within an actuating tube 19, the location of which isdetermined by a screw stop 20. The tube 19 is pressure-sealed from thecarburetor housing 11 through an O ring seal 21. The screw stop 20allows for the flow of fuel 22 from a float chamber 23 through a bore 24into a chamber 25. A fuel regulating screw 26 allows the jet nozzle 18to be moved upwardly in opposition to the force of a tension spring 27,and also to be moved downwardly. Upon further upward rotation of fuelregulating screw 26, jet nozzle 18 is moved downwardly by the tensionspring 27. By means of this arrangement, a basic adjustment of the fuelflow cross-sectional space between jet nozzle 18 and jet needle 17 isprovided. The fuel flows from chamber 12 through bores 28 and 29 intothe hollow interior of the fuel regulating screw 26, and flows fromthere into the jet nozzle 18.

The carburetor float system and the fuel inlet installation of the floatchamber are not illustrated since they do not form a part of theinvention.

A mixing throttle 31 is positioned downstream of slide piston 14 andconsists of a selectively adjustable throttle valve having a valve shaft32 positioned concentrically within the fuel-air mixture outlet conduit13 of the primary system. The membrane 15, in conjunction with the slidepiston 14, forms a movable end wall for the low pressure chamber 33, thelatter of which has a variable volume. The chamber 30 below membrane 15is vented to atmosphere by means of a bore 34. A spring 35 imparts adisplacing force to the slide piston 14 in a direction bending to reducethe flow crosssectional area of the suction conduit. A housing 36 whichis connected to slide piston 14 is adapted to slide within housing 37,the latter of which is connected to carburetor cover 16, so as to effecta centrally oriented movement of the slide piston 14. Within the housinga damping installation 38 is located so as to provide a braking effecton the rapid upward motion of slide piston 14, without restricting therapid downward motion thereof.

In the disclosed embodiment, the mixing throttle 31 is normally closedduring the idling position of the engine. In order to obtain thiseffect, a separate idling system is provided, which essentially consistsof a fuel supply tube 39, fuel conduit 40, fuel regulating screw 41,fuel conduit 42, idling air jet 43, idling fuel-air mixture conduit 44,idling mixture conduit 45, and regulating valve 46. The fuel outlet tubeextends into the fuel in float chamber 23, and includes a calibratedfuel orifice 47 at its lower end. It is also possible to include athrottling device for regulation of mixing the fuel-air quantities inthe idling mixture conduit or idling mixture conduit 44.

The regulating valve 46 includes a valve housing 48, housing cover 49and other standard components. A membrane 50 is stretched between thevalve housing and the cover, and is then connected in a gas-tightrelationship with a closure member 51 by means of membrane plates 52 and53 and a nut 54. The length of the stroke of the membrane plate 53 maybe adjusted on the basis of regulating the mixture quantity. The closuremember 51 is slidably mounted within housing bore 55 at a minimumtolerance. The lower membrane chamber 56 is vented to ambient atmospherethrough a bore 57. The upper membrane chamber 58 is connected to anevacuated or reduced-pressure conduit 60 by a connecting duct 59. Theconnecting duct 59 has a threaded-end connection and includes a bearingseat at its lower end adapted to receive a return valve ball 61, whichis pressed against the seat by means of a spring 62. A bore 63 providesflow connection between the return valve and the membrane chamber 58. Acalibrated bypass connection between the reducedpressure conduit 60 andmembrane chamber 58, which bridges the return valve, is provided bypassages 64 and 65, and cross bore 56. Membrane 50 is subjected to theaction of the suction tube vacuum in opposition to the tensile force ofa membrane spring 67, whereby the pressure extends into membrane chamber58. The membrane spring 67 may be pre-stressed by means of an adjustingscrew 68, the latter of which is sealed from the atmosphere by an O-ringseal 69. The adjusting screw 68 includes a concentrically positionedthreaded bore adapted to receive a smaller adjusting screw 70, which issealed from the atmosphere by an O-ring seal 71 and which forms a limitor stop for the stroke of the valve.

The lower end of the valve housing 48 includes an outer threaded portion72 which facilitates the mounting of the regulating valve 46 onto thecarburetor housing while concurrently providing for the installation andsealing of a conduit-connecting ring 73. The conduit-connecting ring 73is rotatably mounted to facilitate the connection of the idling mixtureconduit 45 from any radial direction. A spacer tube 74 and sealing disc75 allows the conduit-connecting ring 73 to be sealed from theatmosphere.

The lower end of the valve housing 48 includes bore connecting to amixture passage 76 which ends in a conically formed valve seat 77. Atthe side of conduitconnecting ring 73 transfer bores 78 are provided forthe flow of the fuel-air mixture. A closure member 51 is formed into aconical configuration at its lower end.

The connecting point or juncture between the reduced-pressure conduit 60and the fuel-air mixture outlet conduit 13 downstream of mixing throttle31 of the primary system, includes a switching valve 79. The switchingvalve consists of a housing 80, an inlet support 81, inlet connector 81,inlet connector 82', outlet connectors 83, spherical closure member 84,a lever arm 85 having a turn point 86, a tension spring 87, an ironanchor 88 and an electromagnet 89. The switching valve is selectivelyconnected to atmosphere at an inlet point 82. An inlet member 81 isconnected to the mixture outlet conduit 13 of the primary system througha slide member 90 and threaded connector 91. In the disclosedembodiment, the threaded connector 91 is located externally of themechanical operating range of mixing throttle 31. However, theconnecting points may also be located as shown in the discontinuous-linedrawn conduit connections 92 and 93.

The actuation of the electromagnet 89 is provided by means of electronicor electric engine RPM counters 94.

Another embodiment of the regulating valve is disclosed in FIG. 2,wherein the construction is simpler than that of the regulating valve 46shown in FIG. 1.

A valvev housing 111 is connected to a valve cover 113 by screws 112. Amembrane 114 is stretched between the housing and the cover and isconnected in a gas-tight manner with a closure member 115 by means ofmembrane plates 116 and 117, screw 118 and spring plate 119. An uppermembrane chamber 120 is vented to atmosphere through a bore 121. A lowermembrane chamber 122 is connected to a reduced pressure conduit (notshown) through a connecting member 123. A passageway 124 extends fromconnecting member 123 to a return valve 125, having a ball valve 126pressed against a valve seat 128 by means of a spring 127. Connectionbetween return valve and membrane chamber 122 is provided by bore 129. Acalibrated bypass connection between passage 122 and membrane chamber122, which bridges return valve 125, is provided by a passage 130.

The membrane 114 is subjected to the action of the reduced pressurelevel in the suction tube which is conveyed into membrane chamber 122 inopposition to the tensile force of a membrane spring 131.

A threaded connection is provided by a threaded member 133 locatedbetween the valve housing 111 and the lower portion of the valve 132,and wherein the threaded connection concurrently provides for thepretensioning of membrane spring 131.

The closure member 115 is movably supported, at a minimum tolerance,within a bore 134 of the lower portion 132 of the valve. The valveportion 132 includes fuel-air mixture inlet member 135 at its side andat least one mixture outlet passage 136 which extends into aconically-shaped valve seat 137. Similarly, a conical closure member isformed at its lower end. The threaded portion 138 provides for theconnection of the regulating valve to the carburetor housing. Adjustingscrew 139 provides for the adjustment of the stroke of the valve.

When starting up the engine of the vehicle, the mixing throttle 31 isclosed, and slide piston 14 is in its lowermost position, as illustratedin the drawing. The engine RPM counter 94 is closed. Upon ignition ofthe automotive engine, the positive clamp of the RPM counter 94 issubjected to an electrical current and the electromagnet 89 isenergized. The iron anchor 88 is drawn toward the electromagnet so as toswivel pendulum 85 about its pivot 86, in opposition to the tensileforce of the spring 87, into its other operative end position. Thiscauses the movement of the sphericallyshaped closure member 84 in anarcuate motion until the inner aperture of the inlet member 82 isclosed. Through this movement the switching valve 89 connectsreduced-pressure conduit 60 with the fuel-air mixture outlet passage 13of the primary system.

Prior to engine starting, the regulating valve 46 is completely openedin response to the force of membrane spring 67. A reduced pressure isproduced, subsequent to the engine start, in the portion of the fuel-airmixture outlet passage 13 downstream of mixing valve 31, and thepressure drop conveyed into membrane chamber 58. In response to thereduced pressure, the closure member 51 is moved upwardly in oppositionto the force of membrane spring 67. Concurrently, the closure member 51assumes a cross-sectional flow area which guarantees a preciselymeasured quantity of fuelair mixture for idling engine speed.

The reduced pressure produced in mixture outlet passage 13 is alsoconveyed into the mixture passage 76, idling mixture conduit 45, idlingmixture passage 44, fuel passage 42, and fuel passage 40 in the fueloutlet conduit 39. This will cause the idling fuel to be raised towardsthe orifice of the idling chamber 43 in which it is intimately mixedwith the engine idling air and is then sucked by the engine through theaforementioned fuel-air mixture conduits and passages.

As soon as the idling or unloaded engine is loaded through auxiliarycomponents or accessories, the engine RPM is lowered and, concurrently,the pressure increases in mixture outlet passage 13. The increase inpressure is sensed in membrane chamber 58 by means of threaded member91, switching valve 79, reduced pressure conduit 60 and connectingmember 59. In response thereto, the closure member is moved furtherdownwardly so as to provide a larger cross-sectional area for the flowof the idling mixture, and consequently in view of the increased flow ofthe mixture, the engine speed is increased to its required rate.

When the engine is loaded in a sudden manner, the pressure in themixture outlet passage 13 rises just as quickly. This rapid pressureincrease has an immediate effect on the return valve ball 61. The returnvalve opens and thereby allows for an equally rapid pressure increase totake place in membrane chamber 58, so as to provide a rapidly increasedidling mixture quantity, as hereinbefore described. When the engineexceeds its idling rotational speed, for example, during transitionaland full load engine operation, RPM counter 94 interrupts the electricalcurrent energizing electromagnet 89. This will result in the spring 87pulling spherically shaped closure member 84 into the operative positiondisclosed in the drawing. At this point, both membrane chambers 56 and58 are vented to atmosphere, whereby closure member 51 provides for amaximum flow cross-sectional area through the valve. The reducedpressure created in fuel outlet tube 39 does not in itself suffice forthe withdrawal of additional fuel at relatively high suction tubepressures.

When the closing of the mixing throttle is effected in response to thetransitional or full-load operation of the engine, the regulating valve46 remains completely open so as to provide for the required increase inthe fuel-air mixture quantity for the particular operational mode of theengine. This is obtained without the need for intermediate steps, untilthe engine rotational speed again drops to its idling speed. At thattime, RPM counter 94 again closes the electrical circuit, in view ofwhich the switching valve 79 is reversed and regulating valve 46 resumesits normal control operation.

Although the drawing discloses embodiments of carburetors showingpredetermined constructional features, the invention is not limited tothese particular constructions. The invention may be readily applied tonumerous other carburetor constructions. In particular, the invention isadapted for all carburetors utilizing reduced-pressure control fuelsupply systems.

We claim:

1. In a carburetor for automotive engines comprising means for admixingfuel-air mixtures for normal engine operation, including a primary fuelsystem having an admixture suction outlet passageway; a selectivelyactuatable mixing throttle positioned in said passageway; means foradmixing fuel-air mixtures for idling and motive engine operationincluding a calibrated fuel inlet orifice, a calibrated air inlet jetmeans, and an auxiliary and idling secondary fuel-air-mixture inletpassageway joining into said primary fuel system outlet passagewaydownstream of said throttle; the improvement comprising, regulatingvalve means interposed in said secondary fuel-air mixture inletpassageway at the outlet end thereof, said valve having a variable-areaflow passageway, actuating means for said regulating valve, saidactuating means including a closed housing, a flexible membrane in saidhousing dividing the latter into first and second chambers, meansventing said first chamber to atmospheric air, means forming areduced-pressure passageway connecting said second chamber to saidprimary fuel system suction outlet passageway downstream of said mixingthrottle, resilient spring means in said housing, said membrane beingbiased in opposition to the tensile force of said spring means inresponse to the reduced pressure in said suction outlet passageway, areturn valve, said return valve being positioned in the reduced-pressurepassageway interconnecting said housing with said suction outletpassageway, said return valve limiting flow in the direction toward saidhousing when the pressure in said reduced-pressure passageway exceedsthe pressure in said housing, a bypass conduit bridging said returnvalve, said by-pass conduit effecting continuous flow communicationbetween said reduced-pressure passageway and said second membranechamber, and a selector valve disposed in the passageway interconnectingsaid reducedpressure passageway and said primary system suction outletpassageway downstream of said mixing throttle, said selector valvealternatively connecting the reduced-pressure passageway with thesuction outlet passageway and with the ambient surrounding air, thevalve flow area adapted to be automatically increased responsive topressure increases in said primary system suction outlet passageway, anddecreased responsive to pressure drops in said outlet passageway.

2. An improvement as claimed in claim 1, comprising a pair of adjustingmeans extending into said housing, said adjusting means including anouter axially adjustable scr'ew member and an inner screw member sup--ported concentrically within said outer screw member and axially movablerelative thereto, said outer screw member being adapted to effectadjustment of said spring means, and said inner screw memberfacilitating variation of the flow area of said regulating valve betweenpredetermined limits.

3. An improvement as claimed in claim 1, said reduced-pressurepassageway being connected to,the ambient surrounding air upon saidengine exceeding a predetermined rotational speed, and being connectedto the suction outlet passageway at speeds below said predeterminedrotational speed.

4. An improvement as claimed in claim 3, including electromagneticactuating means for said selector valve, said electromagnetic meansbeing connected to electric engine rotational speed counters foractuating said valve in response to a sensed engine rotational speed.

5. An improvement as claimed in claim 1, said selector valve beingactuatable in response to pressures in said suction outlet passageway,whereby said reducedpressure passageway is connected to ambientsurrounding air at predetermined pressures, and connected to the suctionoutlet passageway at higher suction outlet passageway pressures.

6. An improvement as claimed in claim 1, including actuating means forsaid selector valve, said actuating means comprising a housing having amembrane means responsive to pressures in said suction outletpassageway.

1. In a carburetor for automotive engines comprising means for admixingfuel-air mixtures for normal engine operation, including a primary fuelsystem having an admixture suction outlet passageway; a selectivelyactuatable mixing throttle positioned in said passageway; means foradmixing fuel-air mixtures for idling and motive engine operationincluding a calibrated fuel inlet orifice, a calibrated air inlet jetmeans, and an auxiliary and idling secondary fuel-air mixture inletpassageway joining into said primary fuel system outlet passagewaydownstream of said throttle; the improvement comprising, regulatingvalve means interposed in said secondary fuel-air mixture inletpassageway at the outlet end thereof, said valve having a variable-areaflow passageway, actuating means for said regulating valve, saidactuating means including a closed housing, a flexible membrane in saidhousing dividing the latter into first and second chambers, meansventing said first chamber tO atmospheric air, means forming areduced-pressure passageway connecting said second chamber to saidprimary fuel system suction outlet passageway downstream of said mixingthrottle, resilient spring means in said housing, said membrane beingbiased in opposition to the tensile force of said spring means inresponse to the reduced pressure in said suction outlet passageway, areturn valve, said return valve being positioned in the reduced-pressurepassageway interconnecting said housing with said suction outletpassageway, said return valve limiting flow in the direction toward saidhousing when the pressure in said reduced-pressure passageway exceedsthe pressure in said housing, a by-pass conduit bridging said returnvalve, said by-pass conduit effecting continuous flow communicationbetween said reducedpressure passageway and said second membranechamber, and a selector valve disposed in the passageway interconnectingsaid reduced-pressure passageway and said primary system suction outletpassageway downstream of said mixing throttle, said selector valvealternatively connecting the reduced-pressure passageway with thesuction outlet passageway and with the ambient surrounding air, thevalve flow area adapted to be automatically increased responsive topressure increases in said primary system suction outlet passageway, anddecreased responsive to pressure drops in said outlet passageway.
 2. Animprovement as claimed in claim 1, comprising a pair of adjusting meansextending into said housing, said adjusting means including an outeraxially adjustable screw member and an inner screw member supportedconcentrically within said outer screw member and axially movablerelative thereto, said outer screw member being adapted to effectadjustment of said spring means, and said inner screw memberfacilitating variation of the flow area of said regulating valve betweenpredetermined limits.
 3. An improvement as claimed in claim 1, saidreduced-pressure passageway being connected to the ambient surroundingair upon said engine exceeding a predetermined rotational speed, andbeing connected to the suction outlet passageway at speeds below saidpredetermined rotational speed.
 4. An improvement as claimed in claim 3,including electromagnetic actuating means for said selector valve, saidelectromagnetic means being connected to electric engine rotationalspeed counters for actuating said valve in response to a sensed enginerotational speed.
 5. An improvement as claimed in claim 1, said selectorvalve being actuatable in response to pressures in said suction outletpassageway, whereby said reduced-pressure passageway is connected toambient surrounding air at predetermined pressures, and connected to thesuction outlet passageway at higher suction outlet passageway pressures.6. An improvement as claimed in claim 1, including actuating means forsaid selector valve, said actuating means comprising a housing having amembrane means responsive to pressures in said suction outletpassageway.